Charging device

ABSTRACT

A circuit device contains a main circuit structure for main charging and a setting unit incorporated into the circuit structure for setting a weak current. The charging device includes a power-source for supplying a charging current to a secondary battery, an operational amplifier for controlling the supply of the charging current by the power source, and a power element for controlling the supply of the charging current to the secondary battery. Main charging is performed on the secondary battery by supplying a normal current to the secondary battery as the charging current. Trickle charging is performed on the secondary battery by supplying a weak current to the secondary battery as the charging current.

This application claims the benefit of priority to Japanese Patent Application No. 2003-376849, filed on Nov. 6, 2003, herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a charging device, and more particularly, to a charging device capable of performing main charging on a secondary battery by supplying a normal current to the secondary battery as a charging current and of performing trickle charging on the secondary battery by supplying a weak current to the secondary battery as the charging current.

2. Description of the Related Art

Conventionally, there has been disclosed a charging device having a function for mainly charging a secondary battery by supplying a normal current (a large current) to the secondary battery as a charging current and a function for trickle-charging the secondary battery by supplying a weak current to the secondary battery as the charging current.

In general, when it is impossible for a secondary battery to generate the original electromotive force due to the deterioration of the performance of the secondary battery, the trickle charging is performed to restore the original performance of the secondary battery.

FIG. 2 is a circuit diagram illustrating a circuit structure of a conventional charging device 1 having the trickle charging function. The charging device 1 has a main charging circuit 3 for performing the main charging on a secondary battery 2 and a trickle charging circuit 4 for performing the trickle charging on the secondary battery 2.

In the main charging circuit 3, a charging current detecting resistor 7 is provided on the downstream side of a terminal 6 of a power source 5, and the output side of the charging current detecting resistor 7 is connected to an inverting input terminal of an operational amplifier 8 through a resistor r₁. The operational amplifier 8 controls the value of the charging current while detecting the current flowing through the charging current detecting resistor 7.

Meanwhile, a non-inverting input terminal of the operational amplifier 8 is connected to the ground through a resistor r₂. In addition, a resistor r₃ is provided between the non-inverting input terminal of the operational amplifier 8 and the input side of the charging current detecting resistor 7.

Further, the output side of the charging current detecting resistor 7 is connected to an emitter of a power transistor Tr₁ serving as a power element for controlling the supply of the normal current to the secondary battery 2, and a collector of the power transistor Tr₁ is connected to an anode of the secondary battery 2. In addition, a resistor r₄ is provided between a base and the emitter of the power transistor Tr₁.

Furthermore, the base of the power transistor Tr₁ is connected to an emitter of a transistor Tr₂ for controlling a base current of the power transistor Tr₁, and a collector of the transistor Tr₂ is connected to an output terminal of the operational amplifier 8 through a resistor r₅. In addition, a resistor r₆ is provided between a base and the emitter of the transistor Tr₂.

Moreover, an end of a resistor r₇ is connected to the base of the transistor Tr₂, and the other end of the resistor r₇ is connected to a collector of a transistor Tr₃ for controlling the base current of the transistor Tr₂.

An emitter of the transistor Tr₃ is connected to the ground, and a base thereof is connected through a resistor r₈ to a power supply terminal 10 for inputting a base current. In addition, a resistor r₉ is provided between the base and the emitter of the transistor Tr₃.

Further, in the trickle charging circuit 4, a resistor r₁₀ is provided on the downstream side of the terminal 6 of the power source 5, and the output side of the resistor r₁₀ is connected to an emitter of a power transistor Tr₄ serving as a power element for controlling the supply of the weak current to the secondary battery 2.

A collector of the power transistor Tr₄ is connected to the anode of the secondary battery 2, and a diode 11 is provided between a base of the power transistor Tr₄ and the downstream side of the terminal 6 of the power source 5. In addition, an end of a resistor r₁₁, is connected to the base of the power transistor Tr₄, and the other end of the resistor r₁₁ is connected to a collector of a transistor Tr₅ for controlling the base current of the power transistor Tr₄.

A base of the transistor Tr₅ is connected to a base current input terminal 12 through a resistor r₁₂. In addition, a resistor r₁₃ is connected between an emitter of the transistor Tr₅ and an end of the resistor r₁₂ connected to the base thereof. Further, the collector of the transistor Tr₅ is connected to the ground.

According to the charging device having the above-mentioned structure, when the main charging is performed on the secondary battery 2, a base current is supplied to the transistor Tr₃ such that the transistors Tr₃ and Tr₂ and the power transistor Tr₁ are turned on.

Then, a normal current of about 700 mA is supplied as the charging current from the power source 5 to the secondary battery 2 through the emitter and the collector of the power transistor Tr₁, thereby performing the main charging on the secondary battery 2.

In this case, since a base current is not supplied to the base of the transistor Tr₅, the transistor Tr₅ and the power transistor Tr₄ are maintained in an off state.

Subsequently, when the trickle charging is performed on the secondary battery 2, the base current is supplied to the base of the transistor Tr₅ in a state in which the power transistor Tr₁ and the transistors Tr₂ and Tr₃ are off, so that the transistor Tr₅ and the power transistor Tr₄ are turned on.

Then, a weak current of about 50 mA is supplied as the charging current from the power source 5 to the secondary battery 2 through the emitter and the collector of the power transistor Tr₄, thereby performing the trickle charging on the secondary battery 2 (for example, see Japanese Unexamined Patent Application Publication No. 5-284664).

However, in the conventional charging device 1, the main charging circuit 3 is separately arranged from the trickle charging circuit 4. Therefore, the circuits must respectively have expensive power transistors Tr₁ and Tr₄ for controlling the charging current (the normal current or the weak current), which causes an increase in the costs of manufacturing the charging device.

Further, since the power transistors Tr₁ and Tr₄ in the respective circuits through which the charging current flows have high heating values, it is necessary that radiators (not shown) for radiating heat generated from the power transistors Tr₁ and Tr₄ be provided to the power transistors. Tr₁ and Tr₄ separately, which causes an increase in the number of components and an increase in manufacturing costs.

SUMMARY OF THE INVENTION

Accordingly, the present invention is designed to solve the above-mentioned problems, and it is an object of the present invention to provide a charging device capable of reducing the number of power elements required for setting a charging current, thereby achieving a reduction in size and a low manufacturing cost.

In order to achieve the above object, the present invention provides a charging device comprising: a power source for supplying a charging current to a secondary battery; an operational amplifier for controlling the supply of the charging current by the power source; and a power element for controlling the supply of the charging current to the secondary battery. Here, a main charging is performed on the secondary battery by supplying a normal current to the secondary battery as the charging current, and a trickle charging is performed on the secondary battery by supplying a weak current to the secondary battery as the charging current. Further, a circuit structure for the main charging is a main circuit structure, and a setting unit for setting the weak current is incorporated into the main circuit structure.

Therefore, according to the charging device having the above-mentioned structure, a function for controlling the supply of the weak current can be practically complemented with the main charging circuit. Thus, it is possible to reduce the number of control elements required for controlling the charging current.

Further, in the charging device according to the present invention, the setting unit sets the weak current by adjusting an offset of the operational amplifier.

According to the charging device having the above-mentioned structure, it is possible to easily set the weak current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating a charging device according to an embodiment of the present invention; and

FIG. 2 is a circuit diagram illustrating an example of a conventional charging device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a charging device according to an embodiment of the present invention will be described with reference to FIG. 1.

In FIG. 1, the components having substantially the same basic structure as those in a conventional charging device shown in FIG. 2 have the same reference numerals.

As shown in FIG. 1, a charging device 15 according to the present embodiment comprises a power source 5 for supplying the charging current to a secondary battery 2, an operational amplifier 8 for controlling the supply of the charging current by the power source 5, and a power transistor Tr₁ serving as a power element for controlling the supply of the charging current to the secondary battery 2, which is basically the same structure as that of the conventional charging device.

Meanwhile, in the conventional charging device, a main charging circuit 3 for performing main charging on the secondary battery 2 is separately arranged from a trickle charging circuit 4 for performing trickle charging on the secondary battery 2. However, in the charging device 15 according to the present embodiment, these two circuits are integrated into one circuit, and a circuit structure for the main charging is a main circuit structure.

In other words, the charging device 15 according to the present embodiment does not have a power transistor Tr₄, a transistor Tr₅, a diode 11, and resistors r₁₀, r₁₁, r₁₂, and r₁₃ which constitute the conventional trickle charging circuit 4.

In the charging device 15, instead of the above-mentioned elements, a setting unit 16 is provided between a terminal 6 of the power source 5 and an inverting input terminal of the operational amplifier 8 to set a weak current when the trickle charging is performed on the secondary battery 2.

The setting unit 16 performs the setting of the weak current by adjusting the offset of the operational amplifier 8, that is, the input offset voltage (the error voltage) between the input terminals of the operational amplifier 8. In addition, when the volume of the setting unit 16 is small, it is possible to manufacture the charging device 15 at a lower cost.

Further, a resistor r₁₄ is provided between the inverting input terminal of the operational amplifier 8 and the setting unit 16.

Furthermore, a collector of a transistor Tr₆ for switching between the main charging and the trickle charging is connected to the input side of a resistor r₂ connected to a non-inverting input terminal of the operational amplifier 8. In addition, a resistor r₁₅ is connected to a base of the transistor Tr₆, and a resistor r₁₆ is provided between an emitter and the base thereof.

According to this structure, it is possible for the main charging circuit to practically have a function for controlling the supply of a weak current by slightly changing the structure of the main charging circuit, that is, by providing the setting unit 16. Therefore, it is possible to reduce the number of control elements required for controlling the charging current.

Moreover, it is possible to simply set the weak current by adjusting the offset of the operational amplifier.

Next, the effects of the present embodiment will be described.

According to the charging device 15 having the above-mentioned structure, when the main charging is performed on the secondary battery, a base current is supplied to a transistor Tr₃, so that the transistor Tr₃, transistor Tr₂ and the power transistor Tr₁ are turned on.

Further, the base current is supplied to the base of the transistor Tr₆ to turn on the transistor Tr₆.

Then, a normal current of about 700 mA is supplied as the charging current from the power source 5 to the secondary battery 2 through the emitter and the collector of the power transistor Tr₁, thereby performing the main charging on the secondary battery 2.

Subsequently, when the trickle charging is performed on the secondary battery 2, the transistor Tr₆ is turned off, and the offset of the operational amplifier 8 is adjusted by the setting unit 16.

Then, a weak current of about 50 mA is supplied as the charging current from the power source 5 to the secondary battery 2 through the emitter and the collector of the power transistor Tr₁, thereby performing the trickle charging on the secondary battery 2.

Therefore, according to the present embodiment, it is possible to reduce the number of power transistors, which are expensive power elements having a high heating value. Thus, it is possible to obtain the charging device 15 having a low manufacturing cost and to reduce the size of the device.

Furthermore, the present invention is not limited to the above-mentioned embodiment, but variable modifications and changes may be made by one skilled in the art without departing from the scope or spirit of the present invention. 

1. A charging device comprising: a power source to supply a charging current to a secondary battery; an operational amplifier to control the supply of the charging current by the power source; a power element to control the supply of the charging current to the secondary battery; a setting unit corresponding to an adjustable voltage source, the adjustable voltage source coupled to the power source and an inverting input terminal of the operational amplifier and coupled between the power source and the inverting input terminal; a resistor coupled in series with the adjustable voltage source and coupled between the adjustable voltage source and the inverting input terminal; wherein a main charging is performed on the secondary battery by supplying a normal current to the secondary battery as the charging current, and a trickle charging is performed on the secondary battery by supplying a weak current, set by the setting unit, to the secondary battery as the charging current when the main charging is not performed, wherein the power element is turned on during the performance of the main charging and the trickle charging and during transition from the main charging to the trickle charging, and wherein the adjustable voltage source is set so as to adjust an input offset voltage of the operational amplifier so as to set a value of the weak current; and a switch coupled to the operational amplifier and operable to be turned off during the duration of the performance of the trickle charging.
 2. The charging device according to claim 1, wherein the normal current flows through the power element during the performance of the main charging and the weak current flows through the power element during the performance of the trickle charging.
 3. The charging device according to claim 1, wherein the power element comprises a bipolar junction transistor.
 4. The charging device according to claim 1, wherein the switch comprises a bipolar junction transistor.
 5. The charging device according to claim 1, wherein the offset of the operational amplifier comprises an input offset voltage between input terminals of the operational amplifier.
 6. The charging device according to claim 1, wherein one input terminal of the operational amplifier is coupled to the setting unit and the other input terminal of the operational amplifier is coupled to the switch.
 7. The charging device according to claim 6, wherein the setting unit is coupled to the power source and the one input terminal of the operational amplifier which is an inverting input terminal. 